Sheet handling devices of the type used in printing devices, such as electrophotographic printing machines, image input scanning devices, and the like, are well known. They are generally referred to in two categories being document handlers, which are used to transport sheets of material bearing images including, for example, Mylar, vellum, paper and the like, and copy sheet handlers, which transport sheets of similar material which, at least initially, generally are not image bearing. Both types of handlers are frequently employed with electrophotographic printing machines. That is, printers, duplicators and copiers commonly employ sheet handling devices to transport sheets to and from image imprinting stations (e.g., a transfer station in an electrographic printing machine) and image reproduction or imaging input station (e.g., an image input scanning station in an electrophotographic.printing machine). Image input devices which include scanners and the like, also employ sheet handling devices of the type to which this invention relates image bearing sheet to and from an imaging station.
In such devices employing such sheet handlers, inhibiting skew of the sheet transported is an important function to provide acceptable performance. For example, in electrophotographic printing machines employing copy sheet handlers, inhibiting skewing of transported sheets, and thus improving registration of sheets transported through the transfer station, is necessary to provide an output copy sheet having the image imparted thereto appear as desired (e.g., centered and aligned). Failure to provide registration in such cases, generally, results in unacceptable results (e.g., skewed images, images extending off a sheet and the like). Likewise, failure to control skewing and to register sheets bearing images, also known as documents, in document handlers results in the image produced therefrom to be similarly affected. Thus, in single automatic sheet feeding devices, such as document feeders known as semi-automatic document feeders, as well as automatic document feeders, and in sheet feeders known as by-pass sheet feeders, as well as automatic sheet feeders, skew control of the fed sheet is important in many applications, including particularly, those requiring registration of a fed sheet.
Many devices have been developed and techniques are used to register sheets. These devices include side or lateral registration edges in the loading areas of the sheets to be fed. In these cases, the user is required to load sheets for feeding proximate the edge. Active registering devices, such scuffer rollers, cross-rolls and the like have been used to achieve satisfactory results, in most cases. Users thereof who have properly inserted the sheet, achieve such results, provided that the lateral force is not to great to buckle the sheet and great enough to move the sheet. Therefore, many forms of apparatus and devices have been employed in registering and providing registration for sheets and/or documents transported in such sheet handling devices. Nevertheless, in certain cases lateral registration fails, particularly when heavy or special sheets are used. In some instances, this failure can result in the rotation or skewing of the sheet 90.degree. from the desired registration. Besides resulting in misimaging of the sheet (i.e., an image is improperly formed from or on the sheet), these failures can also cause jams and other similar problems.
Applicants have noticed, for example, that in devices using cross-roll and scuffer-roll registering devices which are intended to laterally register a sheet and then have the sheet once registered slide along a lateral registration edge, heavier weight sheets such as label bearing sheets (e.g., AccoBrand labels), as well as vellum and the like, the sheets as fed, often laterally register on the so-called short edge despite the fact that they were to be laterally registered along the so-called long edge when inserted. In fact, the phenomenon appears to occur more frequently the closer the fed sheets are positioned to the lateral side registration edge when initially inserted (e.g., the suggested or preferred method for inserting sheets).
Applicants believe that this error results, generally, from the increased drive force generated on the heavier sheets by the registration devices. That is, for example, in cases of non-adjustable cross rollers, the normal force in the nip on sheets increases as the sheets become thicker. Further, the drag or frictional force engendered by the heavier weight sheets along the lateral registration edge also tend to be greater so that such sheets, instead of slipping in the nip in the lateral direction, tend to rotate or skew. Thus, there exists a need to overcome this type of problem.
The following patents and pending applications may be relevant to this invention:
U.S. Pat. No. 4,984,778 PA1 Patentee: Alexander et al. PA1 Issued: Jan. 15, 1991 PA1 U.S. Pat. No. Re. 33,843 PA1 Patentee: Naramore et al. PA1 Issued: May 17, 1988 PA1 U.S. Ser. No. 07/812,086 PA1 Applicant: Acquaviva et al. PA1 Filed: Dec. 23, 1991
These patents and pending applications may be briefly summarized as follows:
U.S. Pat. No. 4,984,778, incorporated herein by reference discloses a electrophotographic printing machine having a by-pass feeding device with an idler roller to inhibit skewing of a sheet feed along a flat surface of the by-pass feeding device. The idler roller is mounted in the sheet path for rotational contact with a sheet being fed on the centerline of the sheet feeder surface. The idler roll has a high frictional contact surface which is mounted to provide a low drag force in the feeding direction and a high lateral drag force to inhibit skewing.
U.S. Pat. No. Re.33,843 discloses a set of cross-rollers which urge the lateral registration sheets along a registration edge as well as urge the transport of sheets in the process direction. The nip disclosed in this reference is formed by a drive roller and two opposed and separated idler rollers so that a corrugating nip is formed.
U.S. patent application Ser. No. 07/812,086 discloses a variable nip force cross-roll registration device. Specifically, a cross-roll device for laterally registering sheets and driving sheets in the process direction is constructed so that the normal or nip force on sheets in the nip is adjustable to compensate for various weights and characteristics of sheets to be registered by the cross-rolls.
In accordance with one aspect of the present invention, there is provided a lateral sheet registering apparatus for registering sheets transported along a path comprising a lateral registration edge positioned along the path. This aspect of the invention also includes means for driving sheets laterally and along the path so that a lateral edge of a sheet is registered along the lateral registration edge and so that sheets are transported along the path. The invention further includes a gate device positioned in the path opposite the lateral registration edge for engaging an edge of a sheet to oppose rotation of such sheet in the path. The invention can further include mounting the gate device to oppose rotation when engaged by the lateral edge opposite the lateral registration edge but to permit passage of the leading edge of a sheet which engages the gate.
Pursuant to another aspect of the present invention, a sheet handling device comprises a sheet path for receiving sheets and means for transporting sheets along the path in a process direction. The invention according to this aspect also comprises a sheet gate device for exerting an opposed lateral force on sheets transported by the transport means skewing from the process direction and a low force on sheets moving substantially linearly along said path so that sheets are transported substantially freely along the path. The invention can further comprise a second passive sheet gate device position on a side of said path opposed to said first device so that skewing of transported sheets in both rotational (clockwise and counterclockwise) directions is inhibited. This aspect can include positioning the sheet transport means between the opposed first and second gate devices.
Pursuant to still another aspect of this invention, there is provided a method for registering sheets comprising the steps of driving sheets along a path, directing sheets in a lateral direction of a registration edge, providing a registration guide opposed to the registration edge to skewing of the sheet in the path.
In accordance with yet a further aspect of this invention an apparatus for feeding sheets over a surface is provided, which comprises a means for feeding sheets over the surface in a process direction, and a gate device positioned to inhibit skewing of a sheet being feed along the surface. The apparatus of this aspect of the invention can further include a registration edge extending along the surface in the process direction, and means for laterally registering sheets fed by the feeding means along the registration edge.
While the present invention will be described in connection with the preferred embodiment thereof, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all embodiments, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. For a general understanding of the features of the present invention, references should be made to the drawings. In the drawings, like numerals have been used to identify identical elements.